As always, the disclaimer, which this time is, maybe I just don't understand the issue.
However, gonna take a stab at this.
Do you burn candles or happen to smoke in the unit?
Seems I remember, in the deep recesses of my leaky memory that members reported having the ceiling discolor and such when they burned candles in their unit. They were full timers.
Anyway, something else you can digest and then, spit out.
